explanation      blue bibcodes open ADS page with paths to full text
Author name code: fischer
ADS astronomy entries on 2022-09-14
=author:"Fischer, C.E." 

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Title: Towards the Identification and Classification of Solar
    Granulation Structures Using Semantic Segmentation
Authors: Díaz Castillo, S. M.; Asensio Ramos, A.; Fischer, C. E.;
   Berdyugina, S. V.
2022FrASS...9.6632D    Altcode:
  Solar granulation is the visible signature of convective cells at
  the solar surface. The granulation cellular pattern observed in the
  continuum intensity images is characterised by diverse structures e.g.,
  bright individual granules of hot rising gas or dark intergranular
  lanes. Recently, the access to new instrumentation capabilities has
  given us the possibility to obtain high-resolution images, which have
  revealed the overwhelming complexity of granulation (e.g., exploding
  granules and granular lanes). In that sense, any research focused
  on understanding solar small-scale phenomena on the solar surface
  is sustained on the effective identification and localization of the
  different resolved structures. In this work, we present the initial
  results of a proposed classification model of solar granulation
  structures based on neural semantic segmentation. We inspect the
  ability of the U-net architecture, a convolutional neural network
  initially proposed for biomedical image segmentation, to be applied to
  the dense segmentation of solar granulation. We use continuum intensity
  maps of the IMaX instrument onboard the Sunrise I balloon-borne solar
  observatory and their corresponding segmented maps as a training
  set. The training data have been labeled using the multiple-level
  technique (MLT) and also by hand. We performed several tests of the
  performance and precision of this approach in order to evaluate
  the versatility of the U-net architecture. We found an appealing
  potential of the U-net architecture to identify cellular patterns
  in solar granulation images reaching an average accuracy above 80%
  in the initial training experiments.

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Title: Newly formed downflow lanes in exploding granules in the
    solar photosphere
Authors: Ellwarth, M.; Fischer, C. E.; Vitas, N.; Schmiz, S.;
   Schmidt, W.
2021A&A...653A..96E    Altcode: 2021arXiv210700582E
  Context. Exploding granules have drawn renewed interest because of
  their interaction with the magnetic field (either emerging or already
  present). Especially the newly forming downflow lanes developing in
  their centre seem to be eligible candidates for the intensification
  of magnetic fields. We analyse spectroscopic data from two different
  instruments in order to study the intricate velocity pattern within
  the newly forming downflow lanes in detail. <BR /> Aims: We aim to
  examine general properties of a number of exploding granules, such
  as their lifetime and extend. To gain a better understanding of the
  formation process of the developing intergranular lane in exploding
  granules, we study the temporal evolution and height dependence of the
  line-of-sight velocities at their formation location. Additionally, we
  search for evidence that exploding granules act as acoustic sources. <BR
  /> Methods: We investigated the evolution of several exploding granules
  using data taken with the Interferometric Bidimensional Spectrometer and
  the Imaging Magnetograph eXperiment. Velocities for different heights
  of the solar atmosphere were determined by computing bisectors of the
  Fe I 6173.0 Å and the Fe I 5250.2 Å lines. We performed a wavelet
  analysis to study the intensity and velocity oscillations within
  and around exploding granules. We also compared our observational
  findings with predictions of numerical simulations. <BR /> Results:
  Exploding granules have significantly longer lifetimes (10 to 15 min)
  than regular granules. Exploding granules larger than 3.8″ form an
  independent intergranular lane during their decay phase, while smaller
  granules usually fade away or disappear into the intergranular area
  (we find only one exception of a smaller exploding granule that also
  forms an intergranular lane). For all exploding granules that form a new
  intergranular downflow lane, we find a temporal height-dependent shift
  with respect to the maximum of the downflow velocity. Our suggestion
  that this results from a complex atmospheric structure within the newly
  forming downflow lane is supported by the comparison with synthesised
  profiles inferred from the simulations. We found an enhanced wavelet
  power with periods between 120 s to 190 s seen in the intensity and
  velocity oscillations of high photospheric or chromospheric spectral
  lines in the region of the dark core of an exploding granule.

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Title: Interaction of Magnetic Fields with a Vortex Tube at Solar
    Subgranular Scale
Authors: Fischer, C. E.; Vigeesh, G.; Lindner, P.; Borrero, J. M.;
   Calvo, F.; Steiner, O.
2020ApJ...903L..10F    Altcode: 2020arXiv201005577F
  Using high-resolution spectropolarimetric data recorded with the
  Swedish 1 m Solar Telescope, we have identified several instances of
  granular lanes traveling into granules. These are believed to be the
  observational signature of underlying tubes of vortical flow with
  their axis oriented parallel to the solar surface. Associated with
  these horizontal vortex tubes, we detect in some cases a significant
  signal in linear polarization, located at the trailing dark edge of
  the granular lane. The linear polarization appears at a later stage of
  the granular lane development, and is flanked by patches of circular
  polarization. Stokes inversions show that the elongated patch of linear
  polarization signal arises from the horizontal magnetic field aligned
  with the granular lane. We analyze snapshots of a magnetohydrodynamic
  numerical simulation and find cases in which the horizontal vortex
  tube of the granular lane redistributes and transports the magnetic
  field to the solar surface causing a polarimetric signature similar to
  what is observed. We thus witness a mechanism capable of transporting
  magnetic flux to the solar surface within granules. This mechanism is
  probably an important component of the small-scale dynamo supposedly
  acting at the solar surface and generating the quiet-Sun magnetic field.

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Title: Evolution of Stokes V area asymmetry related to a quiet Sun
    cancellation observed with GRIS/IFU
Authors: Kaithakkal, A. J.; Borrero, J. M.; Fischer, C. E.;
   Dominguez-Tagle, C.; Collados, M.
2020A&A...634A.131K    Altcode: 2020arXiv200105465K
  A quiet Sun magnetic flux cancellation event at the disk center was
  recorded using the Integral Field Unit (IFU) mounted on the GREGOR
  Infrared Spectrograph (GRIS). The GRIS instrument sampled the event
  in the photospheric Si I 10827 Å spectral line. The cancellation was
  preceded by a significant rise in line core intensity and excitation
  temperature, which is inferred from Stokes inversions under local
  thermodynamic equilibrium (LTE). The opposite polarity features
  seem to undergo reconnection above the photosphere. We also found
  that the border pixels neighboring the polarity inversion line
  of one of the polarities exhibit a systematic variation of area
  asymmetry. Area asymmetry peaks right after the line core intensity
  enhancement and gradually declines thereafter. Analyzing Stokes
  profiles recorded from either side of the polarity inversion line
  could therefore potentially provide additional information on the
  reconnection process related to magnetic flux cancellation. Further
  analysis without assuming LTE will be required to fully characterize
  this event. <P />Movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936941/olm">https://www.aanda.org</A>

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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
    Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
   C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
   González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
   Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
   A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
   R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V    Altcode: 2018arXiv180507752V
  The solar magnetic field is responsible for all aspects of solar
  activity. Sunspots are the main manifestation of the ensuing solar
  activity. Combining high-resolution and synoptic observations has
  the ambition to provide a comprehensive description of the sunspot
  growth and decay processes. Active region NOAA 12396 emerged on 2015
  August 3 and was observed three days later with the 1.5-meter GREGOR
  solar telescope on 2015 August 6. High-resolution spectropolarimetric
  data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
  photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
  with the chromospheric He I λ1083.0 nm triplet. These near-infrared
  spectropolarimetric observations were complemented by synoptic
  line-of-sight magnetograms and continuum images of the Helioseismic
  and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

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Title: Observations of solar small-scale magnetic flux-sheet emergence
Authors: Fischer, C. E.; Borrero, J. M.; Bello González, N.;
   Kaithakkal, A. J.
2019A&A...622L..12F    Altcode: 2019arXiv190105870F
  <BR /> Aims: Two types of flux emergence were recently discovered
  in numerical simulations: magnetic loops and magnetic sheet
  emergence. While magnetic loop emergence has been documented well in
  recent years using high-resolution full Stokes data from ground-based
  telescopes as well as satellites, magnetic sheet emergence is
  still an understudied process. We report here on the first clear
  observational evidence of a magnetic sheet emergence and characterise
  its development. <BR /> Methods: Full Stokes spectra from the Hinode
  spectropolarimeter were inverted with the Stokes Inversion based on
  Response functions (SIR) code to obtain solar atmospheric parameters
  such as temperature, line-of-sight velocities, and full magnetic
  field vector information. <BR /> Results: We analyse a magnetic
  flux emergence event observed in the quiet-Sun internetwork. After a
  large-scale appearance of linear polarisation, a magnetic sheet with
  horizontal magnetic flux density of up to 194 Mx cm<SUP>-2</SUP>
  hovers in the low photosphere spanning a region of 2-3 arcsec. The
  magnetic field azimuth obtained through Stokes inversions clearly
  shows an organised structure of transversal magnetic flux density
  emerging. The granule below the magnetic flux sheet tears the
  structure apart leaving the emerged flux to form several magnetic
  loops at the edges of the granule. <BR /> Conclusions: A large amount
  of flux with strong horizontal magnetic fields surfaces through
  the interplay of buried magnetic flux and convective motions. The
  magnetic flux emerges within 10 minutes and we find a longitudinal
  magnetic flux at the foot points of the order of ∼10<SUP>18</SUP>
  Mx. This is one to two orders of magnitude larger than what has been
  reported for small-scale magnetic loops. The convective flows feed
  the newly emerged flux into the pre-existing magnetic population on
  a granular scale. <P />Movie attached to Fig. 5 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201834628/olm">https://www.aanda.org</A>

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Title: Flows along arch filaments observed in the GRIS `very fast
    spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
   Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
   Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
   R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
   W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
   J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G    Altcode: 2017arXiv170102206G
  A new generation of solar instruments provides improved spectral,
  spatial, and temporal resolution, thus facilitating a better
  understanding of dynamic processes on the Sun. High-resolution
  observations often reveal multiple-component spectral line profiles,
  e.g., in the near-infrared He i 10830 Å triplet, which provides
  information about the chromospheric velocity and magnetic fine
  structure. We observed an emerging flux region, including two small
  pores and an arch filament system, on 2015 April 17 with the `very
  fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
  situated at the 1.5-meter GREGOR solar telescope at Observatorio del
  Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
  per minute) spectral scans of the solar surface and its potential to
  follow dynamic processes on the Sun. We demonstrate the performance
  of the `very fast spectroscopic mode' by tracking chromospheric
  high-velocity features in the arch filament system.

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Title: Chromospheric impact of an exploding solar granule
Authors: Fischer, C. E.; Bello González, N.; Rezaei, R.
2017A&A...602L..12F    Altcode: 2017arXiv170600770F
  Context. Observations of multi-wavelength and therefore height-dependent
  information following events throughout the solar atmosphere and
  unambiguously assigning a relation between these rapidly evolving
  layers are rare and difficult to obtain. Yet, they are crucial for our
  understanding of the physical processes that couple the different
  regimes in the solar atmosphere. <BR /> Aims: We characterize
  the exploding granule event with simultaneous observations of
  Hinode spectroplarimetric data in the solar photosphere and Hinode
  broadband Ca II H images combined with Interface Region Imaging
  Spectrograph (IRIS) slit spectra. We follow the evolution of an
  exploding granule and its connectivity throughout the atmosphere and
  analyze the dynamics of a magnetic element that has been affected
  by the abnormal granule. <BR /> Methods: In addition to magnetic
  flux maps we use a local correlation tracking method to infer the
  horizontal velocity flows in the photosphere and apply a wavelet
  analysis on several IRIS chromospheric emission features such as
  Mg II k2v and Mg II k3 to detect oscillatory phenomena indicating
  wave propagation. <BR /> Results: During the vigorous expansion of
  the abnormal granule we detect radially outward horizontal flows,
  causing, together with the horizontal flows from the surrounding
  granules, the magnetic elements in the bordering intergranular lanes
  to be squeezed and elongated. In reaction to the squeezing, we detect
  a chromospheric intensity and velocity oscillation pulse which we
  identify as an upward traveling hot shock front propagating clearly
  through the IRIS spectral line diagnostics of Mg II h&amp;k. <BR />
  Conclusions: Exploding granules can trigger upward-propagating shock
  fronts that dissipate in the chromosphere. <P />Movies associated
  to Figs. A.1 and A.2 are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201731120/olm">http://www.aanda.org</A>

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Title: Flow and magnetic field properties in the trailing sunspots
    of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
   C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
   M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
   Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
   R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
   Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V    Altcode:
  Improved measurements of the photospheric and chromospheric
  three-dimensional magnetic and flow fields are crucial for a precise
  determination of the origin and evolution of active regions. We present
  an illustrative sample of multi-instrument data acquired during a
  two-week coordinated observing campaign in August 2015 involving,
  among others, the GREGOR solar telescope (imaging and near-infrared
  spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
  and Interface Region Imaging Spectrograph (IRIS). The observations
  focused on the trailing part of active region NOAA 12396 with complex
  polarity inversion lines and strong intrusions of opposite polarity
  flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
  spectral profiles in the photospheric Si I λ1082.7 nm line, the
  chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
  λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
  provided maps of Doppler velocity and magnetic field at different
  atmospheric heights. We compare quick-look maps with those obtained
  with the “Stokes Inversions based on Response functions” (SIR)
  code, which furnishes deeper insight into the magnetic properties
  of the region. We find supporting evidence that newly emerging flux
  and intruding opposite polarity flux are hampering the formation
  of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
  expected after cessation of flux emergence in proximity to the sunspots.

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Title: Fitting peculiar spectral profiles in He I 10830Å absorption
    features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
   Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
   Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
   Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
   M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G    Altcode: 2016arXiv160300679G
  The new generation of solar instruments provides better
  spectral, spatial, and temporal resolution for a better
  understanding of the physical processes that take place on the
  Sun. Multiple-component profiles are more commonly observed with these
  instruments. Particularly, the He I 10830 Å triplet presents such
  peculiar spectral profiles, which give information on the velocity
  and magnetic fine structure of the upper chromosphere. The purpose
  of this investigation is to describe a technique to efficiently fit
  the two blended components of the He I 10830 Å triplet, which are
  commonly observed when two atmospheric components are located within
  the same resolution element. The observations used in this study were
  taken on 2015 April 17 with the very fast spectroscopic mode of the
  GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
  telescope, located at the Observatorio del Teide, Tenerife, Spain. We
  apply a double-Lorentzian fitting technique using Levenberg-Marquardt
  least-squares minimization. This technique is very simple and much
  faster than inversion codes. Line-of-sight Doppler velocities can
  be inferred for a whole map of pixels within just a few minutes. Our
  results show sub- and supersonic downflow velocities of up to 32 km
  s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
  filamentary structures. The slow component presents velocities close
  to rest.

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Title: Quiet Sun Magnetic Field Evolution Observed with Hinode SOT
    and IRIS
Authors: Fischer, C. E.; Bello González, N.; Rezaei, R.
2016ASPC..504...19F    Altcode:
  We study two physical processes that can be commonly observed in
  the quiet sun and involve temporal evolution of the magnetic field:
  convective collapse and flux cancellation. The aim is to investigate
  the response of the chromosphere to the magnetic events in the
  photosphere below. We have calibrated and aligned a co-spatial and
  co-temporal 3 hour quiet sun time series observed with the Hinode
  SOT (Solar Optical Telescope) and the IRIS (Interface Region Imaging
  Spectrograph) satellites. Convective collapse events are identified in
  the photosphere by inverting spectropolarimetric data and searching for
  magnetic field intensification, preceded by a downflow and accompanied
  by the development of a bright point in Ca II H images. We find a
  corresponding downflow in the low chromosphere as deduced from IRIS
  Mg II k and h spectra and an ensuing oscillatory velocity pattern. We
  use magnetograms in the high photosphere to study pairs of magnetic
  elements involved in flux cancellation and find an increase in the
  entire quasi-continuum of the IRIS Mg II k and h spectrum following
  the flux cancellation process and indicating a substantial energy
  deposit into the lower atmosphere.

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Title: Coimbra Solar Physics Meeting: Ground-based Solar Observations
    in the Space Instrumentation Era
Authors: Dorotovic, I.; Fischer, C. E.; Temmer, M.
2016ASPC..504.....D    Altcode:
  No abstract at ADS

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Title: Unusual Stokes V profiles during flaring activity of a
    delta sunspot
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.; Fletcher, L.;
   Socas-Navarro, H.
2012A&A...547A..34F    Altcode: 2012arXiv1209.0983F
  <BR /> Aims: We analyze a set of full Stokes profile observations of
  the flaring active region NOAA 10808. The region was recorded with
  the Vector-Spectromagnetograph of the Synoptic Optical Long-term
  Investigations of the Sun facility. The active region produced
  several successive X-class flares between 19:00 UT and 24:00 UT on
  September 13, 2005 and we aim to quantify transient and permanent
  changes in the magnetic field and velocity field during one of the
  flares, which has been fully captured. <BR /> Methods: The Stokes
  profiles were inverted using the height-dependent inversion code
  LILIA to analyze magnetic field vector changes at the flaring site. We
  report multilobed asymmetric Stokes V profiles found in the δ-sunspot
  umbra. We fit the asymmetric Stokes V profiles assuming an atmosphere
  consisting of two components (SIR inversions) to interpret the profile
  shape. The results are put in context with Michelson Doppler Imager
  (MDI) magnetograms and reconstructed X-ray images from the Reuven
  Ramaty High Energy Solar Spectroscopic Imager. <BR /> Results: We
  obtain the magnetic field vector and find signs of restructuring
  of the photospheric magnetic field during the flare close to the
  polarity inversion line at the flaring site. At two locations in the
  umbra we encounter strong fields (~3 kG), as inferred from the Stokes
  I profiles, which, however, exhibit a low polarization signal. During
  the flare we observe in addition asymmetric Stokes V profiles at one
  of these sites. The asymmetric Stokes V profiles appear co-spatial
  and co-temporal with a strong apparent polarity reversal observed
  in MDI-magnetograms and a chromospheric hard X-ray source. The
  two-component atmosphere fits of the asymmetric Stokes profiles
  result in line-of-sight velocity differences in the range of ~12 km
  s<SUP>-1</SUP> to 14 km s<SUP>-1</SUP> between the two components in
  the photosphere. Another possibility is that local atmospheric heating
  is causing the observed asymmetric Stokes V profile shape. In either
  case our analysis shows that a very localized patch of ~5″ in the
  photospheric umbra, co-spatial with a flare footpoint, exhibits a
  subresolution fine structure.

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Title: Fast horizontal flows in a quiet sun MHD simulation and their
    spectroscopic signatures
Authors: Vitas, N.; Fischer, C. E.; Vögler, A.; Keller, C. U.
2011A&A...532A.110V    Altcode:
  Numerical simulations of solar surface convection have predicted
  the existence of supersonic horizontal flows in the photospheric
  granulation. Recently, the detection of such flows in data from the
  Hinode satellite was reported. We study supersonic granular flows in
  detail to understand their signatures in spectral lines and to test
  the observational detection method used to identify these flows in
  the Hinode observations. We perform time-dependent 3D radiative MHD
  numerical simulations and synthesize the Fe i 6302 Å spectral lines at
  the resolution of the Hinode data for different viewing angles covering
  the center-limb variation. There is very large variation in the detailed
  shape of the emergent line profiles depending on the viewing angle and
  the particular flow properties and orientation. At the full simulation
  resolution the supersonic flows can even produce distinct satellite
  lines. After smearing to the Hinode resolution sufficient signature
  of supersonic motion remains. Our analysis shows that the detection
  method used to analyze the Hinode data is indeed applicable. However,
  the detection is very sensitive to ad hoc parameter choices and can
  also misidentify supersonic flows.

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Title: Transient events in the solar photosphere at high spatial
    and temporal resolution
Authors: Fischer, C. E.
2011PhDT.......134F    Altcode:
  The research presented in this thesis showcases some of the diverse
  and abundant transient events seen in observed and simulated magnetic
  and velocity ?elds in the solar photosphere. This thesis emphasizes
  the use and understanding of inversion codes to infer the magnetic and
  velocity ?elds from polarized spectral line pro?les. These techniques
  were applied to quiet sun as well as active region observations and
  simulations. The analysis of the small-scale magnetic ?eld evolution,
  as presented in Chapters II and III, sheds light on the evolution
  of the quiet sun magnetism. This brings us closer to understanding
  its dynamics and interplay with the weakly magnetized gas, which is
  suspected to be the root cause for the majority of the heat transfer
  from the photosphere into the chromosphere and corona. The data set
  studied in Chapter IV is intriguing as it shows the magnetic and
  velocity ?eld evolution during a ?are with high temporal cadence. The
  analysis of unusual Stokes pro?les connects the lower photosphere to
  the dynamics in the chromosphere and corona. The last chapter, Chapter
  V, shows that the comparison of highly realistic 3 D simulations with
  observations can tell us more about the underlying physical mechanisms
  of the observed spectral signatures. The study not only con?rms the
  validity of the theoretical model, but also exposes the violent,
  high-speed dynamics present in the photospheric granulation.

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Title: Observations of solar scattering polarization at high spatial
    resolution
Authors: Snik, F.; de Wijn, A. G.; Ichimoto, K.; Fischer, C. E.;
   Keller, C. U.; Lites, B. W.
2010A&A...519A..18S    Altcode: 2010arXiv1005.5042S
  Context. The weak, turbulent magnetic fields that supposedly
  permeate most of the solar photosphere are difficult to observe,
  because the Zeeman effect is virtually blind to them. The Hanle
  effect, acting on the scattering polarization in suitable lines,
  can in principle be used as a diagnostic for these fields. However,
  the prediction that the majority of the weak, turbulent field resides
  in intergranular lanes also poses significant challenges to scattering
  polarization observations because high spatial resolution is usually
  difficult to attain. <BR /> Aims: We aim to measure the difference
  in scattering polarization between granules and intergranules. We
  present the respective center-to-limb variations, which may serve as
  input for future models. <BR /> Methods: We perform full Stokes filter
  polarimetry at different solar limb positions with the CN band filter
  of the Hinode-SOT Broadband Filter Imager, which represents the first
  scattering polarization observations with sufficient spatial resolution
  to discern the granulation. Hinode-SOT offers unprecedented spatial
  resolution in combination with high polarimetric sensitivity. The CN
  band is known to have a significant scattering polarization signal,
  and is sensitive to the Hanle effect. We extend the instrumental
  polarization calibration routine to the observing wavelength,
  and correct for various systematic effects. <BR /> Results: The
  scattering polarization for granules (i.e., regions brighter than
  the median intensity of non-magnetic pixels) is significantly larger
  than for intergranules. We derive that the intergranules (i.e., the
  remaining non-magnetic pixels) exhibit (9.8±3.0)% less scattering
  polarization for 0.2 &lt; μ ≤ 0.3, although systematic effects cannot
  be completely excluded. <BR /> Conclusions: These observations constrain
  MHD models in combination with (polarized) radiative transfer in terms
  of CN band line formation, radiation anisotropy, and magnetic fields.

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Title: Inversions of High-Cadence SOLIS-VSM Stokes Observations
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.
2010ASSP...19..515F    Altcode: 2010mcia.conf..515F
  We have processed full-Stokes observations made with the SOLIS-VSM
  using Fe I 630.15 and Fe I 630.25 nm. The data have high spectral and
  temporal resolution, moderate spatial resolution, and large polarimetric
  sensitivity and accuracy. We use the code LILIA, an LTE inversion code
  written by Socas-Navarro (2001), in order to invert the data in vector
  magnetic fields. The 180-degree ambiguity in magnetic field orientation
  is solved by using the Non-Potential Field Calculation (NPFC) method
  of Georgoulis (2005). The output product are maps of the fullmagnetic
  field vector at the photospheric level, as illustrated in Fig. 1. We
  performed such inversions for observations of active region NOAA 10808
  taken during an X-class flare in September 2005. Details of the data
  processing and the first results are given in the proceedings of the
  Fifth Solar PolarizationWorkshop (ASP Conf. Ser., in press).

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Title: Statistics of Convective Collapse Events in the Photosphere
    and Chromosphere Observed with the HINODE SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
   Keller, C. U.
2009ASPC..415..127F    Altcode:
  Convective collapse, a theoretically predicted process that
  intensifies existing weak magnetic fields in the solar atmosphere,
  was first directly observed in a single event by Nagata et al. (2008)
  using the high resolution Solar Optical Telescope (SOT) of the Hinode
  satellite. Using the same space telescope, we observed 49 such events
  and present a statistical analysis of convective collapse events. Our
  data sets consist of high resolution time series of polarimetric
  spectral scans of two iron lines formed in the lower photosphere and
  filter images in Mg I b<SUB>2</SUB> and Ca II H. We were thus able
  to study the implication of convective collapse events on the high
  photospheric and the chromospheric layers. The physical parameters from
  the full Stokes profiles were obtained with the MERLIN Milne-Eddington
  inversion code. For each of the 49 events we determined the duration,
  maximum photospheric downflow, and field strength increase. We found
  event durations of about 10 minutes and field strengths of up to
  1.65 kG.

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Title: Statistics of convective collapse events in the photosphere
    and chromosphere observed with the Hinode SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
   Keller, C. U.
2009A&A...504..583F    Altcode: 2009arXiv0906.2308F
  Convective collapse, a theoretically predicted process that intensifies
  existing weak magnetic fields in the solar atmosphere, was first
  directly observed in a single event by Nagata et al. (2008, ApJ,
  677, L145) using the high resolution Solar Optical Telescope (SOT)
  of the Hinode satellite. Using the same space telescope, we observed
  49 such events and present a statistical analysis of convective
  collapse events. Our data sets consist of high resolution time series
  of polarimetric spectral scans of two iron lines formed in the lower
  photosphere and filter images in Mg I b{2} and Ca II H, spectral lines
  that are formed in the high photosphere and the lower chromosphere,
  respectively. We were thus able to study the implication of convective
  collapse events on the high photospheric and the chromospheric
  layers. We found that in all cases, the event was accompanied by a
  continuum bright point and nearly always by a brightening in the Ca
  II H images. The magnesium dopplergram exhibits a strong downflow in
  about three quarters of the events that took place within the field
  of view of the magnesium dopplergram. The physical parameters from
  the full Stokes profiles were obtained with the MERLIN Milne-Eddington
  inversion code. For each of the 49 events we determined the duration,
  maximum photospheric downflow, field strength increase and size. We
  found event durations of about 10 min, magnetic element radii of about
  0.43 arcsec and 0.35 arcsec, before and after the event, respectively,
  and field strengths of up to 1.65 kG.

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Title: Vector Magnetic Field Inversions of High Cadence SOLIS-VSM Data
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.
2009ASPC..405..311F    Altcode:
  We have processed full Stokes observations from the SOLIS VSM in the
  photospheric lines Fe I 630.15 nm and 630.25 nm. The data sets have
  high spectral and temporal resolution, moderate spatial resolution,
  and large polarimetric sensitivity and accuracy. We used the LILIA, an
  LTE code written by \citet{fischer_Navarro2001} to invert the data. We
  also applied the non-potential magnetic field calculation method
  of \citet{fischer_Manolis2005} in order to resolve the 180 degree
  ambiguity. The output are maps of the full magnetic field vector at
  the photospheric level. Here we present the first inversions of the
  active region NOAA 10808 during an X-class flare, which occurred on
  13 September 2005.